An inexpensive and accurate way of controlling the movement of a motor-driven vehicle, such as a battery-powered fork lift truck or a remote-controlled carrier, has long been sought. In the interest of efficiency and economy, some such prior vehicles have employed DC motors which are controlled by a single quadrant, open-loop, chopper-type controller. Although such controllers are efficient, they lack the capability of decelerating the vehicle in a regulated manner by the application of reverse motor torque which opposes the motor or by braking. This defect limits their usefulness, since the rate of deceleration is not constant for all loads on the vehicle but varies with the weight of the load and slope on which the vehicle is operating.
Four quadrant controllers have been used to overcome the foregoing defects. However, such controllers are prohibitively expensive for many applications.
Accordingly it is a prime object of the present invention to provide a vehicle propelled by a DC motor operated from a modified single-quadrant, open-loop, chopper-type controller in combination with apparatus for enabling the vehicle to move in either first or second opposite directions within preselected speed boundaries.
Yet another object is to provide a vehicle of the foregoing type in which the vehicle is maintained within the speed boundaries by providing improved apparatus which controls the direction in which motor-generated torque is applied.
Still another object of the present invention is to provide a vehicle of the foregoing type in which the actual speed of the vehicle is compared to a desired speed both during acceleration and deceleration. The speed comparison is employed to maintain the actual speed of the vehicle between upper and lower limits.
Yet another object is to provide a vehicle of the foregoing type in which the DC motor is powered by a battery.